ZCZC AP41
QST de W1AW
Propagation Forecast Bulletin 41 ARLP041
From Tad Cook, K7VVV
Seattle, WA October 13, 2000
To all radio amateurs
SB PROP ARL ARLP041
ARLP041 Propagation de K7VVV
Solar flux and sunspot numbers were down again this week. Average sunspot numbers were down by over 66 points and average solar flux by almost 43 when compared to the previous week.
Last week's bulletin ARLP040 pointed out that the average daily solar flux values for the past three calendar quarters were all about the same, around 182 (180.5 for the first quarter, 182.9 for the second quarter, and 181.9 for the quarter year just completed). The average daily flux for September was 182.1, right at this same value. The past week's average solar flux was 152.6, well below this average.
We are surely at the peak of this solar cycle. Since there is so much daily variation in solar indices, we won't know until much later when the peak actually occurred. This year's values, although higher than last year's, look flat when examining the first nine months of this year.
Solar watchers and HF radio aficionados wonder if during the final quarter the sun will give us some more activity, yielding a later peak. Since the average radio amateur does not actually see many solar cycles during a lifetime, this is a subject of keen interest.
As a young child, the author of this bulletin missed the most exciting sunspot cycle of all, cycle 19 in 1958. As a young ham at age 12 in early 1965, I joined the amateur service at the solar minimum between cycles 19 and 20. The peak of cycle 20 around age 17 was a bit of a disappointment, especially after listening to the stories of the older brethren who gloried in the peak of cycle 19.
Cycles 21 and 22 around age 27 and 38 were more exciting than cycle 20, but one could only hope for another cycle 19 or better. Now at age 48, the probable peak of this cycle is not standing out as anything remarkable, and the question arises of how many more cycles will I get to see, and what will they be like? At an average 11 years per cycle, the probability of seeing much more than two additional solar cycle peaks seems remote, at least at this stage in life. One can only hope. At least by the era of cycle 23 we have so many more tools available than we did in earlier cycles, and with internet connections the availability of these observation and forecasting aids has come right down to the level of the average ham.
We may wish for more sunspots, but along with more activity comes more solar flares and coronal mass ejections which increase polar absorption of radio signals. These events are often interesting to aurora watchers and VHF enthusiasts, but can be a problem for HF communications. October 5 was a day of big geomagnetic disturbance, when the planetary A index reached 96 and there was a sustained period when the K index was seven, indicating a severe geomagnetic storm. The high latitude indices were worse, with Alaska's college A index at 105 and K index as high as eight.
Geomagnetic indices were very quiet from October 6-9. In fact, on October 8 Alaska's college A and K indices were zero for the entire day, which is highly unusual. Solar flux reached a recent short term minimum of 139.6 on October 10.
As this bulletin is written, activity is again increasing. Planetary A index is expected to rise to 35 on Friday, October 13, then hit 15 the next day and 12 for Sunday and Monday. Solar flux values for the same four days are predicted to be 170, 180, 195 and 205. The current rise in geomagnetic activity is due to a full halo coronal mass ejection at the end of the UTC day on October 9. This resulted in an interplanetary shock wave that hit earth's magnetosphere at 2330 UTC on October 12.
Solar flux is expected to peak at 220 around October 18 and 19, and not dip below 200 until October 28. The next short term solar flux minimum is expected around November 5-7. Average solar flux predicted for the next 45 days is 191, which is a bit higher than the average for the first three quarters of this year. Of course, this could be an artifact of the period we are looking at, which includes two upcoming peaks based on the 27.5 day solar rotation.
Sunspot numbers for October 5 through 11 were 145, 127, 94, 128, 106, 95 and 131 with a mean of 118. 10.7 cm flux was 173.8, 158.1, 155.6, 148.9, 140.8, 139.6 and 151.4, with a mean of 152.6, and estimated planetary A indices were 96, 6, 7, 5, 5, 12 and 14 with a mean of 20.7.